The present invention relates to container transfer mechanisms and more particularly to means for effecting the detection of improperly-formed metallic cans.
In recent years the construction of metal cans has changed considerably so that the so-called "two piece" or drawn and ironed can bodies have to a great extent supplanted the previously-used "three piece" bodies. The latter type of can was conventionally formed by rolling a flat strip of stock into a cylinder and sealing the axial seam. A separate, circular end member was then attached to the can to close one end. After the can was filled a third circular end member was then attached to the can to close it. The drawn and ironed two-piece can, on the other hand, comprises unitary side and end walls, so that only the later-applied top member is separable from the body.
The latter type of can body is ordinarily formed through a process termed "drawing and ironing" wherein a rough body blank is first struck into a generally shallow, cup-shaped configuration. The rough cup blank is then deep-drawn, and subsequently forced through a set of annular dies of decreasing diameter to axially elongate the sidewall so as to form a one-piece can body. This is done by urging the cup-shaped blank through appropriate dies by a piston-like ram.
As is well known by those skilled in the art the drawing and ironing process, while it elongates the cylindrical sidewalls of the can body, produces an irregular edge at the mouth of the can. Thus as the ram retreats from its final, extended position and the newly formed can body is stripped from it, the ragged edges of the can body are occasionally bent backwards as they are engaged by the stripping means. In this manner the open edge or mouth of the can is rolled back so as to form a razor sharp, protruding flange. When the can is passed to the succeeding work station, a shearing device ordinarily removes the rough, irregular edge of the can. Occasionally, however, the shearing means or trimmer does not remove all of the rolled-back edge section, particularly where it has been distorted below the area at which trimming occurs.
Aside from this, flaws in the trimming process and other incidents undergone by the can as it is formed and transported during the manufacturing process occasionally leave the semi-finished can with a sharp, protruding edge member known in the art as "rollback". The rollbacks occasionally cause malfunctions and jamming in subsequent processing and/or transporting machinery. While jamming and the like is most undesirable, it is not nearly as expensive or time-consuming as is the result when a rollback encounters coating apparatus of the type commonly used for coating the outsides of the cans.
Conventionally, such a coating apparatus comprises a large roller which spins at high speed and whose periphery is continually supplied with coating material, such as an appropriate lacquer or enamel. The surface of the roller, termed an "application roll" is usually of a soft rubber composition which assures a thorough contact with the surface of the passing cans. Unfortunately, the printing blanket surface is easily damaged by sharp, protruding rollback of a defective can, and, once damaged, proceeds to apply a defective coating to succeeding cans. Aside from the fact that application or coating rolls are relatively expensive to replace, the time involved in dismantling the coating machinery roll and replacing the roll is relatively great. During the replacement time the production of cans necessarily ceases, so that still greater expense is incurred.
While many efforts have been made to develop apparatus for detecting cans having rolled-back edges, to date even the most modest approaches have entailed sophisticated sensing and detecting equipment which is both expensive and susceptible to failure. Accordingly, it will be understood that it would be highly desirable to provide means for detecting the presence of can rollbacks to allow their ejection from the manufacturing stream before they encounter the coating roll of a coating apparatus.
It is therefore an object of the present invention to provide an improved rollback detecting means.
It is another object of the invention to provide a rollback detector which is adapted for use with conventional can transfer and coating equipment.
Still another object is to provide a simple and inexpensive rollback detector which is highly reliable in use.
Yet another object is to provide a safe and effective means for causing the ejection of rolled-back cans from the manufacturing stream.